Synthesis of a FTO Inhibitor with Anticonvulsant Activity - ACS

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Synthesis of a FTO Inhibitor with Anticonvulsant Activity Guanqun Zheng, Thomas Cox, Leah Tribbey, Gloria Zhujun Wang, Paulina Iacoban, Matthew E. Booher, Gregory J. Gabriel, Lu Zhou, Nancy Bae, Joie Rowles, Chuan He, and Mark Jon Olsen ACS Chem. Neurosci., Just Accepted Manuscript • DOI: 10.1021/cn500042t • Publication Date (Web): 18 May 2014 Downloaded from http://pubs.acs.org on May 26, 2014

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ACS Chemical Neuroscience

Synthesis of a FTO Inhibitor with Anticonvulsant Activity Guanqun Zheng†, Thomas Cox‡, Leah Tribbey‡, Gloria Z. Wang†, Paulina Iacoban‡, Matthew E. Booher§, Gregory J. Gabriel§, Lu Zhou¶, Nancy Bae , Joie Rowles‡, Chuan He†, Mark J. Olsen*,‡ †

Department of Chemistry, University of Chicago, 929 E. 57th St., Chicago, IL 60637

‡

Department of Pharmaceutical Sciences, College of Pharmacy – Glendale, Midwestern

University, 19555 N. 59th Ave., Glendale, AZ 85308 §

Department of Chemistry and Biochemistry, Kennesaw State University, 1000 Chastain Rd.,

Box 1203, Kennesaw, GA 30144 ¶

School of Pharmacy, Fudan University, 826 Zhangheng Rd., Shanghai, 201203 P.R. China Department of Biochemistry, Arizona College of Osteopathic Medicine, Midwestern

University, 19555 N. 59th Ave., Glendale, AZ 85308 KEYWORDS Anticonvulsant, FTO, N6-methyladenosine, RNA, microRNA, epilepsy

ACS Paragon Plus Environment

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ABSTRACT We describe the rationale for and the synthesis of a new class of compounds utilizing a modular approach that are designed to mimic ascorbic acid and to inhibit 2-oxoglutarate-dependent hydroxylases. Preliminary characterization of one of these compounds indicates in vivo anticonvulsant activity (6Hz mouse model) at non-toxic doses, inhibition of the 2-oxoglutaratedependent hydroxylase FTO, and expected increase in cellular N6-methyladenosine. This compound is also able to modulate various microRNA, an interesting result in light of the recent view that modulation of microRNAs may be useful for the treatment of CNS disease. INTRODUCTION Epilepsy is a chronic disorder of abnormal electrical activity in the brain characterized by recurrent unprovoked seizures.(1) Treatment with traditional antiepileptic drugs (AED) is not effective for about 30% of patients, and pharmaco-resistant epilepsy remains a current clinical challenge. Agents that modify the disease progression, antiepileptogenics,(2) may have some advantages over traditional AEDs. Recently, the need for novel agents for the treatment of pharmaco-resistant epilepsy and the development of antiepileptogenics has been emphasized.(3-5) We sought to design and synthesize novel antiepileptogenic compounds that induce the production of erythropoietin (Epo) in the CNS. Our rationale was based on reports of the neuroprotective(6) and antiepileptogenic effects(7) of Epo. Additionally, Epo has been demonstrated to induce beneficial mood swings in patients suffering from depression,(8, 9) which is the most frequent co-morbidity with epilepsy.(10) Developing a single agent with both anti-


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epileptogenic and anti-depressant effects would enhance value as a novel agent for the treatment of epilepsy. Epo production is controlled through the HIF (hypoxia inducible factors) pathway.(11) HIF proteins are transcription factors that control the expression of hypoxia-induced genes to overcome the crisis of hypoxia. The enzyme prolyl-4-hydroxylase 2 (PHD2) has a critical role in this pathway by targeting HIF-1α for proteasomal degradation; this enzyme is active under usual, non-hypoxic conditions. PHD2 is a member of a family of oxygen requiring, 2-oxoglutarate (2OG) dependent hydroxylases that utilize non-heme iron in the catalytic site and ascorbic acid as cofactor.(12) We have recently proposed an antiepileptogenic mechanism in which inhibition of PHD would permit HIF proteins to function and to induce the expression of Epo and other hypoxia-induced genes.(1) Therefore, our rational drug design was to inhibit PHD which would lead to increased endogenous expression of Epo in the CNS. Our compounds did not, however, inhibit PHD but rather a related enzyme family member, FTO (Fat Mass and Obesity). We describe the synthesis and initial characterization of this FTO inhibitor and demonstrate anticonvulsant activity in an animal model of pharmaco-resistant epilepsy.(3, 4) We selected the aminohydroxyfuranone core (1, Figure 1) as a scaffold for developing PHD inhibitors due to the similarity to ascorbic acid (2, Figure 1) which is known to have antioxidant(13, 14) and PHD-binding properties.(15) Tetronic acid derivatives (3, Figure 1) are related to ascorbic acid and have been shown to significantly inhibit cyclooxygenase and lipoxygenase,(16) activities that might be desirable to modulate the neuroinflammation that occurs during epileptogenesis.(17) However, the scaffold of 3 does not readily permit for the elaboration of additional functional groups for PHD inhibition. We reasoned that adding an additional functional group to the terminal amine of 1 to yield a 2,5 disubstituted 3,4-dihydroxyfuran


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scaffold, 4, would result in a family of ascorbic acid mimics that would also be able to mimic 2OG due to the presence of an amide or sulfonamide. Compounds from scaffold 4 still resemble ascorbic acid, allowing for the potential for these high polar surface area compounds to utilize the sodium-coupled vitamin c transporters 1 & 2 (SVCT1 & 2) for BBB penetration. Ascorbic acid mimics that are capable of utilizing transporters may resolve the conundrum of developing BBB-penetrating 2-OG mimics, due to the strong negative charge of 2-OG needed for recognition of the PHD active site, yet simultaneously possessing an appropriate LogP and low polar surface area characteristics required of BBB penetrating agents (see below). These compounds may also target other related enzymes such as FIH, ASPH, TET-1 and FTO.

Figure 1. Scaffold selection for prolyl-4-hydroxylase inhibitors based upon a core dihydroxyfuran moiety. X = C or S, y = 1 or 2. 1, aminohydroxyfurananones, 2, ascorbic acid, 3, arylhydroxytetronic acids, 4, 2,5-disubstituted-3,4-dihydroxyfurans. The crystal structure of PHD2(18) provided crucial information for our drug design by revealing specific molecular interactions between the 2-OG ligand, the critical active site iron, and Arg383 that is involved in 2-OG recognition. The 2,5 disubstituted 3,4-dihydroxyfuran scaffold enables a modular approach to developing PHD inhibitors as illustrated in Figure 2. The concept was to


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position an aryl group as module A which is tolerated in known PHD2 inhibitors.(19) In module B, the aminohydroxyfuranone ring core can serve as an iron chelating moiety to interact with the active site Fe and also provide a hydrogen bond acceptor to a critically positioned water molecule.(18) Module C is a carbonyl or sulfonyl adaptor to serve as a hydrogen bond acceptor for Arg383, as well as a synthetic handle for attaching Module D. The presence of different modules is expected to result in different 2-oxoglutarate/ascorbic acid mimics with different enzyme inhibition selectivities.

Figure 2. Conceptual design of prolyl-4-hydroxylase inhibitor utilizing a modular approach with a core dihydroxyfuran moiety. RESULTS AND DISCUSSION Synthesis of the targeted compounds is illustrated in Scheme 1. The synthesis begins with the condensation of potassium cyanide, glyoxal bisulfite addition product, and an aryl aldehyde originally explored by Dahn and co-workers,(20) and is followed by an acetylation or sulfonylation to give compounds 6-7. Acetylation with acetic anhydride results exclusively in the O-acetyl product 6b, while reaction with methylsulfonyl chloride and ethylsulfonyl chloride result in both 6c and 7c, the result of O- and N-sulfonylation respectively. Reaction with


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phenylsulfonyl chloride results exclusively in the 6e O-sulfonylation product. The compounds synthesized are indicated in Table 1.

Scheme 1. a KCN, glyoxal bisulfite addition product, Na2CO3; b Ac2O, RT; c K2CO3, ClSO2CH3, THF, reflux; d K2CO3, ClSO2CH2CH3, THF, reflux; e K2CO3, ClSO2C6H5, THF, reflux.

Table 1. Prepared Compounds.

Cmpd 5 6b 6e 7c 7d

X C S S S

y 1 2 2 2

R CH3 C6H5 CH3 CH2CH3

Computational methods were utilized to evaluate the feasibility and potential metabolic liability of proposed compounds prior to synthesis. Selected physico-chemical and biological properties were calculated using StarDrop Version 5.3.1 Build 202, and are shown in Tables 2&3. These calculations indicate that the compounds 7c and 7d have solubility and LogP values that are consistent with good BBB penetration, but have polar surface area values that are above what is usually considered favorable for passive diffusion across the BBB. However, compounds with


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similar high polar surface areas have been reported to cross the blood brain barrier by utilization of the SVCT2.(21) Since the dihydroxyfurans mimic ascorbic acid, it is reasonable to predict that they may penetrate the BBB via SVCT2. Table 2. Calculated physico-chemical properties. Cmpd 5

MW 225.6

TPSA(Å2)[a] 72.55

LogS 3.93

LogP 1.07

6b

267.6

78.62

2.90

1.07

6e

365.7

95.69

1.33

1.67

7c

303.6

99.77

3.28

1.74

7d

317.6

99.77

3.08

2.11

[a]

Total Polar Surface Area

Table 3. Predicted biological activities Log(BB) Cyp3A4 Cyp2D6 hERG pIC50

Cmpd

BBB

5

+

-0.03

0.85

medium

3.83

6b

-

0.11

0.82

medium

3.68

6e

-

-0.13

0.75

medium

4.27

7c

-

-0.18

0.64

low

5.05

7d

-

-0.15

0.51

medium

5.18


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Biological screening of perspective antiepileptogenic compounds is extremely challenging, and there is no generally accepted series of experiments to evaluate antiepileptogenic potential. Our compounds were screened for anticonvulsant activity in mice by the NIH/NINDS/ASP, using the following models: maximal electroshock (MES), subcutaneous metrazole (scMET), and 6Hz. The compounds showed little to no protection in the MES and scMET models (data not shown). However, most compounds were effective in the 6Hz model (Table 4). These results clearly demonstrate in vivo anticonvulsant activity and therefore likely CNS penetration of the compounds, possibly via ascorbic acid transporters.(21) The ASP screened these compounds for general CNS toxicity using the rotarod method and little to no toxicity was found (Table 5). Based on predicted cytochrome P450 oxidation, 7d was selected for advancement to the quantitative 6Hz model. Analysis using this method indicated that the7d anticonvulsant EC50 was 18 mg/kg, the toxic EC50 was 347 mg/kg, resulting in a safety ratio (toxic EC50/anticonvulsant EC50) of 19.3, indicating reasonable safety (Table 6). To put these data into perspective, 7d had a higher safety ratio than all commercially available AEDs tested except for levetiracetam.(22) It is also interesting to note that levetiracetam, a very useful agent to treat epilepsy, was also not active in the MES and scMET models.(22) Table 4. Activity in the 6Hz model. Cmpd[a] 0.25h[b] 0.5h 1h 2h 4h (N/F) [c] (N/F) (N/F) (N/F) (N/F) 5 1/4 0/4 1/4 1/4 0/4 6b 2/4 0/4 1/4 0/4 1/4 6e 1/4 0/4 2/4 2/4 2/4 7c 1/4 4/4 4/4 3/4 4/4 7d 1/4 3/4 2/4 3/4 3/4 [a] Compounds were injected in 0.1% methylcellulose i.p. at 100mg/kg. [b]Time after i.p. injection. [c]N is the number of protected animals, F is the total number of animals in trial group.


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Table 5. Toxicity in the rotarod model. 1h 2h 4h Cmpd[a] 0.25h[b] 0.5h (N/F) (N/F) (N/F) (N/F)[c] (N/F) 5 0/4 0/4 0/4 0/4 0/4 6b 0/4 0/4 0/4 0/4 0/4 6e 0/4 0/4 0/4 0/4 0/4 7c 0/4 1/4 2/4 0/4 3/4 7d 0/4 0/4 0/4 1/4 0/4 [a] Compounds were injected in 0.1% methylcellulose i.p. at 100mg/kg. [b]Time after i.p. injection. [c]N is the number of animals displaying toxicity, F is the total number of animals in trial group.

Table 6. Activity of 7d in the quantitative 6Hz and toxicity model. Test[a]

Time Dose N/F[b] (Hours) (mg/kg) 6Hz 1.0 1.0 0/8 6Hz 1.0 2.5 1/8 6Hz 1.0 5.0 5/8 6Hz 1.0 10.0 5/8 6Hz 1.0 25.0 11/16 6Hz 1.0 50.0 4/8 6Hz 1.0 100.0 10/16 6Hz 1.0 200.0 6/8 Toxicity 8.0 100.0 0/8 Toxicity 8.0 200.0 2/8 Toxicity 8.0 300.0 3/8 Toxicity 8.0 500.0 5/8 Toxicity 8.0 750.0 7/7 [a] Compound was injected in 0.1% methylcellulose i.p. [b]N is the number of animals displaying protection or toxicity, F is the total number of animals in trial group.

Compounds 7c and 7d were further tested for activity in the HIF pathway. Treatment of HeLa cells with dimethyl N-oxalylglycine, a global inhibitor of 2-OG enzymes, inhibits PHD, stabilizes HIF1α,(23) and turns on the expression of HIF-induced genes including Epo.(24) HeLa cells were treated with or without 7c and 7d, and then analyzed for stabilization of HIF1α and HIF2α by Western blots. Stabilization of HIF1α or HIF2α was not seen, nor were Epo levels


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changed (data not shown), indicating that 7c and 7d do not inhibit PHD under these experimental conditions. We considered that our compounds may be interacting with enzymes related to PHD that also utilize 2-OG. Examination of the structure of 7c and 7d with the conformations of the inhibitor N-oxalylglycine (NOG) from crystal structures of PHD,(18) FIH,(25) Jumanji-C containing histone demethylase JMJD2A,(26) and FTO(27) suggested that FTO was a reasonable target. The conformation of NOG in PHD, FIH, and JMJD2A is nearly identical, and is entirely planar as illustrated in Figure 3. In contrast, NOG from FTO is significantly twisted out of the plane, and results in O5 being nearly 1.76Å above the plane containing the amide bond. Due to the presence of the sulphonamide in both 7c and 7d, a sulfone oxygen can be nearly 2.47Å above the plane of the iron chelating dihydroxyfuran moiety. We hypothesized that 7c and 7d might inhibit FTO, and that the key distinguishing feature of FTO inhibition versus PHD inhibition is the presence of a non-planar hydrogen bond acceptor capable of mimicking the terminal carboxylate oxygen of 2-OG at the FTO active site.


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A

B

PHD & FIH

FTO 4

4

O 1

O

O

5

O

1

1

HN

2

O

O

O

O N H O

3

O O O

O

C Cl

O HO

HO Cl

O

Dihedral Angle = -126.78

Dihedral Angle = -178.23

O O

HN

2

3

O

1

O

5

O NO H

1.76Å

O O S N H OH

O OH O S O NH

2.47Å

Figure 3. A. Conformational analysis of NOG from crystal structures 3HQR and 2XUM for PHD and FIH. B. Conformational analysis of NOG from 3LFM for FTO. C. Conformational analysis of 7d. The compounds 7c and 7d were tested for the ability to inhibit purified FTO.(28) The results indicate that FTO was inhibited by each compound, with IC50 of 4.9µM and 8.7µM respectively. These values are similar to those reported for broad-spectrum 2-OG oxygenase inhibitors, 3methylthymidine (IC50 8.3 µM),(29) N-oxalylglycine (IC50 44 µM),(29) and rhein (IC50 21 µM).(30) To assess the cellular effect of FTO inhibition, total HeLa cell mRNA was quantified for the presence of N6-methyladenosine (m6A). FTO is a nucleic acid demethylase that prefers RNA m6A(28) over other substrates such as N3-methyluracil and N3-methylthymine.(31) A 9.3% increase in m6A was observed following treatment of 25µM 7d (p

Synthesis of a FTO Inhibitor with Anticonvulsant Activity - ACS

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